What are supplementary tax returns?

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Under the Spanish General Tax Law (LGT), taxpayers may submit supplementary declarations and self-assessments within the filing period or afterwards, provided the Tax Administration’s right to determine the tax debt has not become time-barred. Those filed after the deadline are late (section 122.1 LGT).

A supplementary self-assessment completes or amends an earlier one where it results in a higher amount payable or a lower refund or credit. If the correction benefits the taxpayer, the applicable route is rectification of the self-assessment or, where the tax rules so provide, a corrective self-assessment (sections 122.2 and 120.3–4 LGT). The Tax Administration may verify filed self-assessments under section 120.2.

Where a supplementary return is filed late without a prior administrative request, the surcharge regime in section 27 LGT may apply. Filing a declaration or self-assessment may interrupt the limitation period when it is a formal, verifiable act aimed at determining or self-assessing the debt. The general limitation period is four years, but its start, interruption and any special rules depend on the right and circumstances (sections 66–68 LGT). Each supplementary filing does not automatically give the Administration a new five-year period.

The filing and payment deadlines, forms and channels depend on the rules for the particular tax. There is no general rule requiring amounts due under a supplementary return to be paid at a Tax Agency office. If a return is filed within the statutory filing period, the applicable tax rules govern how to replace or correct it and whether an option made with the return may be changed (section 119.3 LGT).